X-ray filament with balanced emission

ABSTRACT

An X-ray filament having a transversely extending portion with coils substantially along its entire length and a longitudinally extending portion attached to each of the ends of the transversely extending portion, the longitudinally extending portions each having a plurality but substantially lesser number of coils therein than does the transversely extending portion. A pair of electrical support leads substantially heavier than the wire from which the filament is made are connected to the ends of the longitudinally extending portions.

United States Patent John '1. Perry Weateheeter;

Robert M. Cooney, Chicago, both of 111. 827,203

May 23, 1969 Dec. 28, 1971 Picker Corporation White Plains, N.Y.

Inventors Appl. No. Filed Patented Assignee X-RAY FILAMENT WITH BALANCED EMISSION 4 Claims, 1 Drawing Fig.

313/55, 313/344 Int. Fl H0lj 35/08 Field of Search 313/55, 56,

[56] References Cited UNITED STATES PATENTS 2,290,226 7/1942 Dumond 313/330 X 2,671,867 3/1954 Atlee 313/330 X 2,812,462 11/1957 Maltby et al. 313/330 X 3,158,513 11/1964 Janssen et al. 313/330X Primary Examiner-James D. Kallam Assistant Examiner-Andrew J. James Attorney-Buckhorn, Blore, Klarquist and Sparkman ABSTRACT: An X-ray filament having a transversely extending portion with coils substantially along its entire length and a longitudinally extending portion attached to each of the ends of the transversely extending portion, the longitudinally extending portions each having a plurality but substantially lesser number of coils therein than does the transversely extending portion. A pair of electrical support leads substantially heavier than the wire from which the filament is made are connected to the ends of the longitudinally extending portions.

PATENTEU [[028 97! JOHN T. PERRY ROBERT M. COONEY INVE'NTORS. BY

BUCKHO/W, BLORE, Kmmu/sr a SPAR/(MAN ATTORNEYS X-RAY FILAMENT WITH BALANCED EMISSION BACKGROUND OF THE INVENTION The conventional cathode filament used in the cathode structure of an X-ray tube comprises a coiled wolfram wire extending substantially transversely of the cathode structure to the end portions of which filament are connected a pair of substantially heavier electrical support leads.

The electron emission from such prior filaments, however, has not been substantially uniform over the transverse length of the filament but tends to be lower at the end portions because of the lower temperatures of such end portions.

Accordingly it is the primary object of the present invention to provide an improved filament for X-ray cathodes in which the emission therefrom will be substantially uniform along a greater proportion of the coil length than was heretofore possible.

A further object of the present invention is to provide an improved filament for X-ray cathodes, the construction of which filament will prevent loss of heat into the filament supports, thereby to achieve a more uniform profile of emission than was heretofore possible.

SUMMARY OF THE INVENTION The filament of the present invention comprises a transversely extending portion having a plurality of coils substantially along its entire length and a longitudinally extending portion attached to each of the ends of the transversely extending portion, each of the longitudinally extending portions having a plurality but substantially lesser number of coils therein than does the transversely extending portion. A pair of electrical support leads made from wire which is substantially heavier than the wire from which the filament is made, are connected to the ends of the longitudinally extending portions.

The heated coils in the longitudinallyextending portions minimize conduction of heat into the leads from the ends of the transversely extending portion, thus maintaining a more uniform temperature over the length of the transversely extending portion. The structure results in an electron emission substantially more uniform over the length of the filament than was heretofore possible.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing illustrates a portion of an X-ray tube having a cathode structure and an anode structure, the cathode structure including a filament made in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, the numeral designates an X- ray diffraction tube having a cathode structure I2 and an anode structure 14 mounted in a suitable enclosure I6. The cathode structure 12 includes an elongate mounting tube 18 positioned in the discharge end of which is the improved filament 20 of the present invention.

The filament 20 has a portion 22 extending transversely of the enclosure 16 and which portion includes coils 24 substantially along its entire length. The filament 20 also comprises portions 28 extending longitudinally of the enclosure I6, each of which longitudinally extending portions 28 also includes a plurality of coils 26. The number of coils 26 in the longitudinally extending portions 28, however, are substantially less than the number of coils 24 in the transversely extending portion 22. The spacing of the coils 26 in the portions 28 may differ substantially from that of the coils in the transversely extending portion 22.

The ends of each of the longitudinally extending portions 28 of the filament 20 are connected to electrical support leads 32 which are made of substantially heavier wire than is the filament 20.

Prior filaments having coils extending substantially along their transverse length tend to lose heat more rapidly from then end portions and thus are maintained at a lower temperature than the center portion. As a result, the electron emission from the center portion has occurred at a greater rate than from the end portions. This is undesirable because the resulting focal spot on the anode is not uniform. In a filament of the invention, the coils 26 in the longitudinally extending portions 28 retard heat loss by conduction from the ends 30 of the transversely extending portion 22. This is accomplished by adjusting the number of coils 26 and the spacing between them in the longitudinally extending portions 28. Thus the filament temperature is maintained substantially uniform throughout the length of its transverse portion, and as a consequence, the electron emission is substantially uniform over the length of the filament. For example, in a conventional filament, the emission will be at acceptable levels only over about one-half the filament length at its center portion, the emission dropping off undesirably at the opposite ends. With the filament of the invention, acceptable emission levels can be maintained over about percent of the length of the filament.

A preferred form of filament in accordance with the present invention was constructed from a length of pure wolfram wire 0.0075 inch in diameter. It had a transverse length of 0.580 inch, and in such transverse length there were 31.5 coils or turns made on an 0.024 inch diameter mandrel. The longitudinally extending portions of the filament were each 0.125 inch long and each has three coils or turns also made on an 0.024 inch diameter mandrel. The three coils in each of the longitudinally extending portions were found not to add significantly to the emission from the cathode assembly, and the emission level was found to be substantially flat or constant over approximately 80 percent of the transverse length of the filament.

If the emission from a filament constructed in accordance with the present invention manifests slight peaks at the ends of the transverse length thereof as a result of emission from the supplemental coils in the longitudinally extending portions, such peaks may be reduced by varying the number of coils or by other well known expedients.

We claim:

I. An X-ray tube comprising a longitudinally spaced anode and cathode; and

a filament in said cathode, said filament comprising a transversely extending portion having a plurality of coils therein substantially along its entire length, and

a longitudinally extending portion attached to each of the ends of said transversely extending portion, each of said longitudinally extending portions having a plurality of coils therein.

2. An X-ray tube as set forth in claim I, in which the number of coils in said longitudinally extending portions of said filament are substantially less than the number of coils in said transversely extending portion.

3. An X-ray tube as set forth in claim I, in which said transversely extending portion and said longitudinally extending portions of said filament are formed from the same diameter wire.

4. An X-ray tube as set forth in claim 1, in which said coils in said transversely extending portion and said coils in said longitudinally extending portions of said filament are of constant diameter. 

1. An X-ray tube comprising a longitudinally spaced anode and cathode; and a filament in said cathode, said filament comprising a transversely extending portion having a plurality of coils therein substantially along its entire length, and a longitudinally extending portion attached to each of the ends of said transversely extending portion, each of said longitudinally extending portions having a plurality of coils therein.
 2. An X-ray tube as set forth in claim 1, in which the number of coils in said longitudinally extending portions of said filament are substantially less than the number of coils in said transversely extending portion.
 3. An X-ray tube as set forth in claim 1, in which said transversely extending portion and said longitudinally extending portions of said filament are formed from the same diameter wire.
 4. An X-ray tube as set forth in claim 1, in which said coils in said transversely extending portion and said coils in said longitudinally extending portions of said filament are of constant diameter. 